Telemetry to measure time taken to display kernel dropdown list when user clicks button or hits command...

[DonJayamanne]

Either update or create a seprate telemetry to monitor perf of time to display the dropdown list of kernels when user attempts to select a kernel.

Right now we seem to be using the measures for time taken to search for kernels as a measure of time taken to display the kernel picker UI (this isn't entirely accurate).

[IanMatthewHuff]

Validated:
Info Python Extension: 2020-02-18 09:01:37: Telemetry Event : DATASCIENCE.SELECT_LOCAL_JUPYTER_KERNEL Measures: {"duration":12} Props: {"common.os":"win32","common.platformversion":"10.0.18363","common.extname":"ms-python.python","common.extversion":"2020.3.0-dev","common.vscodemachineid":"someValue.machineId","common.vscodesessionid":"someValue.sessionId","common.vscodeversion":"1.42.1"}